Merck said on Wednesday the US Food and Drug Administration had placed a clinical hold on three multiple myeloma studies testing its Keytruda in combination with other medicines for the blood cancer after more deaths were reported in patients receiving the Merck immunotherapy. The rare setback for Keytruda sent Merck shares more than 1 percent […]

Merck said on Wednesday the US Food and Drug Administration had placed a clinical hold on three multiple myeloma studies testing its Keytruda in combination with other medicines for the blood cancer after more deaths were reported in patients receiving the Merck immunotherapy.

The rare setback for Keytruda sent Merck shares more than 1 percent lower.

Merck has been on a roll with the medicine, jumping to the front of the pack of companies with new immuno-oncology drugs, particularly after Keytruda extended survival as an initial treatment for advanced lung cancer, by far the largest oncology market. Bristol-Myers Squibb had been the perceived leader in the field until last year, when its Opdivo failed to match Keytruda’s lung cancer success.

Merck last month said it had stopped enrolling patients in the trials testing Keytruda in combination with standard multiple myeloma regimens including Celgene Corp drugs. The decision was taken after independent safety monitors observed more deaths in patients receiving the Keytruda combination than in the control groups in two of the studies.

The FDA said based on available data the risks of combining Keytruda with either of the Celgene medicines outweigh any potential benefit for patients with multiple myeloma.

The trials were testing Keytruda with either Revlimid or Pomalyst and dexamethasone against the regimens without Keytruda.

All patients who were receiving Keytruda in combination with a Celgene drug will no longer take the Merck drug.

The clinical hold does not apply to other studies with Keytruda, Merck said. The drug, which helps the immune system fight cancer by blocking a protein tumors use to avoid detection, is currently being tested in hundreds of combination trials in a wide variety of cancers.

So far, Keytruda is only approved for one type of blood cancer, classical Hodgkin lymphoma. But Merck has had a string of successes in solid tumor cancers with approvals for advanced melanoma, advanced bladder cancer and a type of head and neck cancer, in addition to lung.

In May, Keytruda became the first cancer drug to win U.S. approval based on a patient’s specific genetic traits, regardless of where in the body the disease originated, known as microsatellite instability-high cancer.

Merck shares fell to $63.40 in extended trading from a New York Stock Exchange close at $64.16.